1. Is 90mm a wide angle lens or a telephoto lens?

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2. If I’m taking a picture of a building, why would my perspective change if I switch from a wide angle lens to a telephoto lens?

3. Name one reason why I would want to take a portrait up-close with a wide angle, and one reason why I would want to take a portrait far away with a telephoto.

Week 8 Quiz

LensesLenses define 2 important things:• Angle of view (focal length)• Aperture

Film/SensorWhere the light is recorded

LensBends the light

Trajectory of lightSubject

Source of light

FocusingA look at the overall camera system

Light converges at sensor

Light converges past sensor

Light converges before sensor

Result:

‘In focus’

‘Out of focus’

Result:

‘In focus’

Circle of confusionImage doesn’t have to

perfectly converge. If it converges within a “circle of

confusion”, it is still ‘in focus’

‘In focus’

‘Out of focus’

In focus

Out of focusOut of focus

•Things at a certain distance are “in focus” (perfectly sharp)•The further from this distance, the blurrier things are•There is a range of distance where things are ‘sharp enough’ to be considered ‘in focus’. This range is known as the “depth of field”

Amount of Blur

Depth of field

Depth of fieldRange that is ‘in focus’

Focus point

Near limit of focusFar limit of focus

Film/SensorWhere the light is recorded

Circle of confusionMaximum non-convergance

allowed to be ‘in focus’

Depth of field

Circle of confusion

When using a bigger lens (larger aperture), the depth of field shrinks

Depth of field

Circle of confusion

Longer subject distances mean larger depth of field range

Circle of confusion

Longer focal lengths mean smaller depth of field range

Depth of field

A = aperture f-number (e.g. f5.6)f = focal length (e.g. 50mm)d = distance to subject (e.g. 3000mm)c = circle of confusion (e.g. .02mm)

Factors to note:Smaller apertures (larger f-number) gives larger depth of fieldShorter focal length gives larger depth of fieldLonger distance to subject gives larger depth of fieldLarger circle of confusion gives larger depth of field

(Acd)-f2Ac(fd) =fieldof Depth 24

0 2 4 6 8 10 120

Aperture

As aperture increases, depth of field increases

0 50 100 150 200 250 300 3500

Focal length (mm)

As focal length increases, depth of field decreases.At very wide focal lengths (ultrawide), depth of field increases rapidly

Translating focal length into angle of viewAngle of view Focal length - 35mm Focal length - 1.5x APS-C Focal length – 1/1.7”

62.01° 36mm 24mm 8mm

Actual focal length35mm equivalent focal length

0 5000 10000 15000 20000 25000 300000

100000

150000

200000

250000

Subject distance

As subject distance increases, depth of field increasesAt very long subject distances, depth of field increases rapidly (hyperfocal distance)

0 50 100 150 200 250 3000

Focal Length

For a constant magnification, depth of field is roughly the same across all distance/focal length combinations

Uses of large depth of field

Landscape/scenery

Architecture Small depth of fieldMacro

Uses of small depth of field

Portraits

Flowers

Sports

Isolation

Bokeh: quality of out-of-focus “blur”

Focal length rangesTwo types of lenses: Zooms (variable focal length) and Primes (fixed focal length)

Different focal lengths are useful for different things

Large aperture zooms• As large as f/2.8 aperture• Expensive! Canon 17-55 f2.8

Canon 70-200 f2.8$1139

Focal length rangesTwo types of lenses: Zooms (variable focal length) and Primes (fixed focal length)

Different focal lengths are useful for different things

Large aperture primes• Very large apertures (f2, f1.8, f1.4, f1.2)• (Mostly) Cheaper than large aperture zooms• Fixed focal length (angle of view)

Nikon 85mm f1.8$419

Canon 50mm f1.4$316

Canon 50mm f1.8$83

Portrait AssignmentFocus on the following elements:• Lighting (direction, intensity)• Vantage point (camera direction, setting, background)• Perspective (subject distance vs. focal length)• Depth of field• Directing the subject (poses, props, expression)

Before shooting: Login to the gallery, choose 3 photos and evaluate each of these elementsWhat was done, how it worked out, and how you would do it

• Lighting (direction, intensity)• Vantage point (camera direction, setting, background)• Perspective (subject distance vs. focal length)• Depth of field• Directing the subject (poses, props, expression)

Portrait AssignmentFocus on the following elements:• Lighting (direction, intensity)• Vantage point (camera direction, setting, background)• Perspective (subject distance vs. focal length)• Depth of field• Directing the subject (poses, props, expression)

Before shooting: Login to the gallery, choose 3 photos and evaluate each of these elementsWhat was done, how it worked out, and how you would do it

Partner up with someone in the class (right now, or post on the forums)

Come up with your own themeYou’ll have to present your photoshoot and talk about each of the elements

If you want, shoot in RAW (we’ll be talking about processing after Spring Break)

1. Is 90mm a wide angle lens or a telephoto lens?

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